Laboratory: Fire prevention

bench_fire

firemen_lab

  • The lab technician was cleaning metal parts with Hexane. The parts were places in a beaker of Hexane which was on a hot plate. Nearby was a plastic wash bottle filled approximately 50% with Hexane. A flash fire occurred. The fire was successfully put out with a small ABC extinguisher. The white powder in the picture is the extinguishing agent. The heat from the hot plate caused a small drip from the wash bottle. The small release vaporized and the vapor was ignited by the hot plate. Fortunately, there were no injuries and no significant damage.

  • This was not the case in the fire in the second figure. This fire occurred when a boiling pot on a thermal distillation apparatus failed. A student was injured and the laboratory and building suffered major losses. The research and teaching building was shut down for a week during the academic year.

Fire prevention requires understanding the properties of flammable chemicals and controlling the chemicals such that the fire tetrahedron is not allowed to form (see below). While the Safety Data Sheet and the container label are the primary sources of information, that information is not helpful if the students or scientists involved do not understand concepts such as flash point, vapor pressure or static electricity.
There are some basic rules for handling all flammable chemicals. Following the rules, along with other safe laboratory work procedures will help prevent fires.

Keep away from heat, sparks, and sources of ignition

The small fire in the first example would not have happened if the ignition source had been properly controlled. The major fire in the second example was ignited by the transformer which powered the heating mantle. The transformer was in the hood immediately adjacent to the distillation apparatus.

Keep containers closed, except when in use

The plastic wash bottle and the open beaker were both “open containers”. If the beaker had been covered or the wash bottle was removed to a hood when not in use, the fire would not have happened.

Ground all metal drums and transfer vessels

Whenever more than about 8 liters of a non-conductive liquid is transferred, sufficient static electricity can accumulate on the system to act as an ignition source. Whenever 4 or more liters of a non-conductive fluid is transferred, the entire system, including the source, the receiver, and all transfer piping must be grounded and electrically joined together (“bonded”) to achieve a common voltage potential.

Maintain adequate ventilation

General laboratory ventilation is adequate to remove routine vapor emissions. A laboratory hood is usually sufficient to prevent the accumulation of ignitable concentrations of flammable vapors during a laboratory procedure. If these assumptions are not clearly correct, the adequacy of ventilation must be investigated. Failure to do so could result in a flash fire or explosion.

Use labelled and proper safety cans and cabinets

Putting the “wrong chemical in the wrong vessel at the wrong time” is a major cause of chemical incidents. Proper labeling, and forming the habit of looking at the label prevents incidents.

Maintain and use vapor suppressing solvent spill control media

While activated charcoal is the most powerful vapor-suppressing material, it is generally to dusty for use in a laboratory or process plant. Products such as the TRIVOREX® Powder or vapor-suppressing pads (for very small spills) work very effectively and do not create excessive mess. All lab personnel should be familiar with proper procedures for the clean-up of small spills.

Maintain and know how to use ABC fire extinguishers

Neither the technician nor the student in the examples above knew how to use a fire extinguisher. A student in the lab of the first incident used the extinguisher. No attempt was made to put out the fire in the second incident. The fire overwhelmed the building fire suppression system for a period of time, but finally the building system did quench the fire. Approximately 40,000 liters of fire suppression water had to be removed from the building.

Minimize quantity of flammable chemicals in work area

Fire codes dictate the maximum amount of flammable liquids which can be used or stored in a fire zone. In many circumstances these amounts are too much. Minimizing the amount of flammable liquids (fuels) reduces both the potential for and severity of a fire.

Review your fire prevention procedures

fire tetrahedron

Review your fire response preparedness. Make certain everyone understands the information needed to prevent fires. Keep the concepts of the “fire tetrahedron” in mind as your work with any ignitable material. Failure to follow these ideas can result in a fire, with injuries, loss of property, loss of work, and damage to the environment.

Neal Langerman - On line 09/03/2008

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